Hi!
When I tried to insert a block using the context menu, I was confronted with the error message Trying to insert a block on non-empty cell. The process is,
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Click a block with ctrl + right click


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Select another block with ctrl + left click

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Select orient. If selected block has a block on the direction, the error occur.

Uncaught exception: Trying to insert a block on non-empty cell at (15,15,15)
I think the menu should be closed once another block is selected, so that this bug will be fixed.